Protein Intake and Plasma Phenylalanine Concentrations in Maternal Phenylketonuria

Abstract

LEARNING OUTCOME: To define how protein intake is related to plasma phenylalanine concentrations and birth outcome in maternal phenylketonuria Women with phenylketonuria (PKU) who do not follow a low phenylalanine (PHE) diet are at high risk of giving birth to offspring with problems such as microcephaly, mental retardation, congenital heart disease and low birth weight. The Maternal PKU Collaborative Study (MPKUCS) examined the efficacy of a low PHE diet in preventing such problems. The diet is prescribed to meet the Recommended Dietary Allowances for pregnancy and is based on medical foods which provide a PHE-free source of protein. The subjects were women with PKU who had plasma PHE concentrations greater than 600 μmol/L at enrollment and who were treated with a low PHE diet. Weekly blood PHE concentrations were determined and the average PHE exposure was calculated. Monthly diet records on 249 women were collected and analyzed for 19 nutrients. Nutrient intake was correlated with average PHE exposure and birth outcome using Spearman correlation coefficients. The best predictor of offspring birth length, weight and head circumference was the number of weeks gestation after which maternal plasma PHE concentration was consistently below 600 μmol/L. Protein intake was negatively correlated with average PHE exposure during pregnancy (p=0.0001). Women with the highest protein intakes had the lowest plasma PHE concentrations and the best birth outcomes. When managing nutritional therapy of pregnant women with PKU, adequate protein intake should be emphasized. Since medical foods are the primary source of protein in the maternal PKU diet, every effort should be made to ensure adequate medical food intake.